Spark plugs have been the traditional means to ignite the fuel/air mixture inside combustion chambers of gas turbine engines for many decades. The spark plugs were housed in struts extending across the compressed air plenum, between the combustor casing and the combustion chamber liner. The liner is subjected to extreme high temperatures and associated thermal growth whereas the casing is subjected to relatively cool compressed air and therefore to much less thermal growth. The end of the strut mounted to the liner needed to accommodate the relative thermal growth of the liner, which was achieved by a floating collar but nonetheless produced fretting and required regular maintenance.
In more recent years, spark plugs have been replaced by laser igniters. The laser igniters were at least partially housed in the strut and typically had a focusing lens, or window, exposed to soot from the combustion chamber. Henceforth, although the laser igniters procured some advantages over spark plugs, they continued to require maintenance, such as maintenance required from the fretting of the strut and exposure of optical components to soot. Accordingly, there remained room for improvement in addressing the level of maintenance required from the fretting and exposure to soot.